Barriers of this type are in widespread use, for example in the Paris subway. Such a barrier has three legs fixed to a hub whose axis of rotation is at about 45.degree. to the vertical.
One of the legs takes up a horizontal position obstructing a passage while the other two are in a retracted position within the thickness of the turnstile stand. Normally the support hub is prevented from rotating, thereby preventing non-authorized users from passing. However, a user may be allowed to pass by unlocking rotation of the leg-supporting hub, releasing the turnstile to rotate through one-third of a turn each time a user passes, generally after the user has been recognized by an agent or after a pass has been recognized automatically.
In general, the hub supporting the three legs is mounted on the stand so that the horizontal leg obstructs the passage at a height of about 800 mm above the ground. This type of barrier suffers from the defect of being easy to get past, either by ducking under the leg or by jumping over it, if necessary by taking a purchase on the two stands on either side of the passage.